Apparatus for heat treatment of material, particularly infra-red radiation of a continuous paper web in a paper machine

ABSTRACT

Apparatus (1) for treatment of a continuous paper web (18) in a paper machine by means of infra-red radiation, comprising, in a parallel relation to the paper web, infra-red heaters (17) and protection panes. The protection panes (12) are arranged by way of a series of separate panes overlapping each other and forming ventilation gaps (27), which are directed substantially in parallel relation to the web in the same direction or in two opposite directions.

The present invention relates to an apparatus for heat treatment ofmaterial, particularly infra-red radiation of a continuous paper web ina paper machine and is more closely defined in the preamble of claim 1.

It is previously known to expose e.g. a continuous paper web in a papermachine to infra-red radiation for drying the web wholly or partially.Hereby, the infra-red radiation creates a great heat potential, whichentails the need for cooling the radiation and protection of the paperweb against smear spots and other polution, the risk of fire and unequaldrying. For achieving such a protection, supply and/or exhaust aircurrents are used, which affect the radiation and the paper web. Thesecurrents are provided to bring about guaranteed cooling, but withoutminimizing the efficiency of the drying process and without adverselyaffecting the path of the web, respectively. These demands have, so far,not been met by previously known techniques.

Such apparates do often comprise a s.c. counter reflector provided tothrow back part of the heat radiation having passed through the paperagainst same. It is desirable, for making the drying process moreefficient, to arrange the counter reflector as close to the paper web asis possible. Hitherto, the counter reflector had, however, to bearranged at relatively large distance to the paper web, for variousreasons, which brought about decreased efficiency. The same applies tothe reflector itself with the radiation source which, mainly because ofsecurity reasons, had to be arranged at relatively large distance fromthe paper web in previously known apparates, which rendered a clearlyworse degree of efficiency. Of major importance in this connection is,however, the guidance of the web, which so far, for certain combinationsof paper weight, structure, moisture contents, free length in thedirection of the web etc, has been adversely affected by reflectorsarranged too closely nearby, because of negative affects of the coolingair currents on the web. Further drawbacks of known techniques are greatwaste of power, difficulties to perform maintenance and service,maintaining an equal degree of efficiency and need for frequent service.

The object of the invention is to provide an improved apparatus of thekind as initially defined, which avoids the said drawbacks. A superiorpurpose of the invention is to provide a basis for using the componentscomprised by the apparatus as efficiently as possible, to increase thelevel of efficiency substantially and to provide, in spite of theseadvantages, the same or even increased security. A further object of theinvention is to improve techniques in this field in various otherrespects.

These objects are achieved according to the invention in that anapparatus of the kind as initially defined substantially ischaracterized by the features of the characterzing clause of claim 1.Thanks to these features, it is possible to arrange the radiator withthe reflector very close to e.g. a paper web, namely, according toobtained test results, at 20 mm distance between protective glas panesand a paper web, which is to compare with app. 50 mm according topreviously known technique. In such a way, a much more extensive dryingis, of course, obtained and the level of efficiency may be increasedfurther by arranging even the counter reflector closer to the web. Inspite of these features, it is possible to ensure an advantageous webguiding, which is not or only negligibly affected by e.g. air currents.Said features do also safeguard, that the apparatus is, as far aspossible, kept free from dirt. The lack of substantial free air currentsbrings about a degree of purity which is unknown so far, and whichconsiderably increases both efficiency and safety.

Furthermore, the concept of overlapping protective panes offers theadvantage, that tolerances and thermical expansion won't affect thetightness of the assembled glas surface.

Further characteristics of and advantages with the invention arerevealed by the following specification with reference to theaccompanying drawings which, schematically, illustrate a preferred,though not limiting example.

FIG. 1 is a cross-sectional view of an apparatus according to theinvention,

FIG. 2 is a sectional view according to line A ./. A in FIG. 1illustrating conditions at relatively low pressure,

FIG. 3 is a view corresponding to FIG. 2 at relatively high pressure,

FIG. 4 is a partial view of the embodiment according to FIG. 2 or anembodiment between FIG. 2 and 3,

FIG. 5 is a view corresponding FIG. 4 of a modified embodiment,

FIGS. 6 and 7 are a side elevational view and a top plan view,respectively, of a preferred embodiment of a pane holder.

In FIG. 1, 1 designates a preferred embodiment of an apparatus accordingto the invention in its entirety. The apparatus comprises e.g. anelongated exterior housing 2 provided in one end wall 3 with an inlet 4,side walls 5 and a top side 6 with an outlet 7. Lowermost, the exteriorhousing shows an opening 8 occupying substantially the underside andlaterally limited by narrow flanges 9, which preferably are provided ata border 10 extending all-around the side walls 5 and the end walls 3and permitting easy and complete access to the interior of the exteriorhousing.

From below, pane holders 11 are attached to the flanges 9 and carrypanes 12, which in principle cover the opening 8. Appearance andfunction of the pane holders will be more closely described inconnection with FIG. 2-5.

Between the end walls 3, there extends an interior housing 13 with topside 14, side walls 15 and a lower opening 16, which is occupied byinfra-red heaters 17 with reflectors (not shown) inserted into theinterior housing and facing a paper web 18, which is guided outside ofthe panes 12 and parallel to these. The web runs to the left or to theright in FIG. 1.

The side walls 15 of the interior housing are arranged at distance fromthe side walls 5 of the exterior housing in order to provide exhaust airpassages 19, which connect a lower supply air zone 20 between saidheaters 17 and the inside of the panes 12 to an upper merging passage 21between the top sides 6 and 14, which merging passage extends into saidout let 7 to lead away the exhaust air. The supply air and the exhaustair are thus guided in a closed system.

Herein, the supply air is preferably filtered before entering theapparatus according to the invention. The exhaust air may wholly orpartly be used in e.g. heat exchangers or other energy using devices.The exhaust air is supplied in a pure state and does not requirefiltering, accordingly. The housings are suitably made of stainlesssteel.

On the reverse side of the paper web, there is preferably provided acounter reflector 22, which is previously known per se and has theobjective to throw back the major part of the radiation which haspenetrated the paper web and in this way heat up the latter even on thatside which is turned away from the heaters 17. Thanks to the invention,even the counter reflector can be arranged relatively close to the paperweb, e.g. 20 mm from same, while that distance previously was app. 50mm.

As revealed by FIG. 1, the supply air is distributed from the inlet orinlets 4 around and/or through the heaters 17 and through the supply airzone 20, which thus becomes a cooling zone, towards both sides 5. Thepressure of the supply air may easily be adjusted in that the inlet 4 isconnected to a fan 23 generating excess pressure and/or in that theoutlet 7 is connected to a fan 24 generating a vacuum. Possibly, a fanfor the exhaust air is unnecessary thanks to the invention.

According to another, substantial feature of the invention, the panes 12are arranged in series throughout the length of the exterior housing,i.e. at right angle in relation to the sheet plane of FIG. 1. The panesbridge the entire distance between the juxtaposed pane holders 11 in onepiece and have thus a length of 250-600 mm, preferably app. 350 mm. Thewidth is preferably 100-300 mm only, suitably app. 150 mm. This widthshows up in FIGS. 2 and 3, which also reveal another important featureof the invention, namely that the longside regions 25, 26 of the panesoverlap each other. The overlap is such that gaps 27 are formed whicheither all of them point in the same direction or, for instance,commencing at the center of the apparatus, point in opposite directions.

The pane holders 11 are shown schematically only in FIGS. 2 and 3. Theymay be provided in a continuous way for receiving any number of panes ore.g. a pane each. They are furnished with a groove 29 for receiving thepane or panes. This groove may be so wide, that an overlap is possiblewithin the groove, i.e. the groove is at least twice as wide as thethickness of the panes. It is also possible to provide several grooves29, one for each pane, and/or may the grooves and/or the pane holders beoblique in a way as illustrated by the grooves 29 in FIG. 6.Furthermore, within or outside of the grooves and at their lower endthere may be stop means 30, which limit insertion of the panes in thisdirection. According to a special embodiment of the invention, thesestop means may be provided to form or prolong or limit or affect,respectively, wholly or partly said gaps 27. A preferred embodiment isshown in FIGS. 6 and 7, where the holders form, in the direction ofinclination, a lower projection 31, on which there is provided to restan upper projection 32 arranged at the opposite side of the holders. Thefront edge of the lower projection 31 and the matching edge of the upperprojection 32 may preferably be oblique for easier fitting in.

The edges of the panes entering the grooves 29 may be furnished withsome kind of lining, packing or the like (not shown), which may have acertain elasticity for desirable adjustment or regulation of the widthof the gaps 27. In principle, at low pressure drop via the gaps 27, thepanes attain a position according to FIG. 2, where supply air leaksthrough the gaps 27 in a controlled way. The flow points in the samedirection and somewhat away from the panes and soewhat towards the paperweb, which may be advantageous in certain cases. Mostly, a controlaccording to FIG. 3 or closely to FIGS. 3, 4 or 5 may, howver, to bepreferred. Herein, most a relatively large pressure drop prevails viathe gaps 27, which decrease in width simultaneously due to this pressuredrop, as the superposed pane area 25 is pushed down towards theunderlying area 26 of the adjacent pane by the pressure. In this way, anautomatic self-adjustment is always achieved, which cannot be affectedeven by wear and tear as time goes by. Within the gap itself, a lowerpressure arises, thanks to which the pane areas superimposing each otherare so to speak sucked towards each other. Through the very narrowremaining gap, high velocity air currents 35 are pushed out in parallelrelation to that side of the panes which faces the paper web, which panesides simultaneously are kept clean and cooled thanks to these currents,which benefit, due to velocity and substantial momemtum, from the s.c.coanda effect, i.e. that an air current is sucked towards a confinementby the arising vacuum. The volume of these air currents is however, solittle, that the guidance of the web is not adversely affected in anyway. An advantage in this connection is also, that the partial currentsassist each other by a combined sucking and pushing effect. The power ofa partial stream may therefore not be chosen in such a way, that thestream or current easily and quickly can leave the region between panesand paper web, which likely could give rise to turbulences entailinginterferences in the guiding of the web. Very favourable is the laminarflow of air between panes and paper web. At high pressure drop, the flowdirection is, as has been said, substantially parallel to the panes,which may be further improved by narrow and possibly long gaps, whichare achievable by choosing longer overlap zones. At low pressure drop,it may be favourable to direct the air currents slightly more towardsthe paper web for better breaking up a steam layer surrounding the web.This flow pattern may accordingly be controlled, among other means, bycontrol of the pressure drop. Naturally, there may be provided specialmeans for increasing/decreasing the width of the gaps, e.g. by way ofs.c. pivot points 36, around which the panes may turn or be turnedsimultaneously increasing or decreasing the gap width. Another means maybe shaping the pane edges within the overlap zones e.g. by bevellingand/or curving which, to a certain degree, may have the effect ofdiffusing and/or increasing velocity. The pane edges may also, in theseareas, be ground in a special way to form, in combination, a ceratindesired jet design and thus render an increased length of throwrespectively velocity at a certain difference of pressure. Even in thisway, the length of the gaps may be controlled.

Thanks to the invention, panes and infra-red heaters may readily be forinstance exchanged, which is a favourable spin-off effect of theinvention, which is to be compared with removing a large pane with manypoints of attachment, large weight and other discomfort.

It will be appreciated, that the panes may be arranged alternately atdifferent levels which, admittedly, will result in pairs of air currentspointing in opposite directions, which currents may, however, bedesigned differently or is it possible to obstruct one gap formation.

I claim:
 1. Apparatus (1) for heat-treatment of a web of material of acontinuous paper web (18) in a paper machine, comprising a number ofinfra-red heaters (17) arranged in parallel relation to the web andseparated from the web by protection glass (12), a cooling air systembeing provided to cool the infra-red heaters and the protection glass,characterized in that the protection glass (12) is provided as a seriesof separate panes overlapping each other and forming ventilation gaps(27), which are directed substantially in parallel relation to the web.2. Apparatus according to claim 1, characterized by an elongate exteriorhousing (2) with an inlet (4) for the web in any end wall (3), sidewalls (5) and a top (4) and with an outlet (7) for the web in anopposite end wall (3), an opening (8) occupying substantially the entireunderside and being laterally confined by flanges (9) at the side walls(5).
 3. Apparatus according to claim 2, characterized in that betweenthe end walls (3) there extends an interior housing (13) having a top(14), side walls (15) and a lower opening (16), which is covered byinfra-red heaters (17) with reflectors, in said interior housing,oriented to face the web (18) through the glass panes, the side walls(15) of the interior housing being arranged at distance from the sidewalls (5) of the exterior housing to form therebetween exhaust airpassages (19), which interconnect a lower supply air zone (20) betweensaid heaters (17) the panes (12) with an upper exhaust passage (21)between the tops (6) and (14), the exhaust passage being connected tothe outlet (7) for removing exhaust air.
 4. Apparatus according to claim2, characterized by a counter reflector (22) which is located 20 to 33mm from the web remote from the heaters (17).
 5. Apparatus according toclaim 2, characterized in that the panes (12) are arranged in seriesalong the length of the exterior housing, that the panes each bridgingthe entire distance between opposite pane holders (11) attached to theflanges (9) of the side walls, and that the pane holders (11) are eachdesigned to hold at least one pane.
 6. Apparatus according to claim 5,characterized in that the pane holders are provided with grooves (29) toreceive the panes, the grooves having such a width, that the overlaptakes place within the grooves.